A package of semiconductor has been generally performed such that a circuit element is soldered to a die pad electrode portion (island portion) of a lead frame by die bonding and then, it is molded using resin. In a case of the circuit element such as a semiconductor device having large heat release, solder (hereinafter, referred to as “a solder material”) has been used as brazing agents for the die bonding.
As the solder material, the solder material basically made of (Sn—Pb)-based solder material has been used in the past. Among them, the solder material made of primarily Sn (Sn with Pb of 5 percent by mass)-based solder material (hereinafter, a reference to an alloy will be carried out by deleting “percent by mass”), which has a relative high melting point of about 300 degrees C., has been used. This is because a heating condition of the solder material (a mounting solder material) when mounting the surface-mount component on the printed circuit board is from 240 to 260 degrees C., and they are heated for some seconds through 100 seconds so that the die-bonding solder material is required not to be melted.
When the circuit element operates, its temperature rises and when the circuit element does not operate, its temperature returns to the normal temperature thereof, so that any bonded portion by the solder material suffers a large temperature change. On the other hand, since the circuit element and the die pad electrode portion of the lead frame have different coefficients of thermal expansion from each other, the bonded portion by the solder material suffers any stresses repeatedly following the temperature changes based on the difference in the coefficients of thermal expansion. Fatigue based on this repeated stresses may cause cracks to occur in the bonded portions by the solder material. Accordingly, accompanying the crack extension, reliability of electric connection in the bonded portion by the solder material may deteriorate.
From these reasons, solder material in which metal, in minuscule quantities, such as Ag, In, Bi and/or Cu is contained in a composition of almost (Pb-5Sn) contains have recently been proposed.
However, if device having a very different coefficient of thermal expansion is bonded using these as the die-bonding solder material, a stress suffered to a bonded portion by the solder becomes too heavy so that a problem such that any remarkable improvement effect on heat cycle performance cannot be seen has been arisen.
In addition to this, any influence of Pb, which is contained in the (Sn—Pb)-based solder material, to a human body has recently been gotten popular, so that it has become a problem that a pollution of global environment or an influence to living things by a disposal of manufactured articles containing Pb should be reduced.
In order to reduce environmental pollution or the like, lead-free solder material has been required. Accordingly, as the mounting solder material to be used when performing a surface mounting of surface-mount component onto a circuit board such as a printed circuit board, the lead-free (Pb-free) solder material has been recently used.
Further, until recently, as the die-bonding solder material, which is used when bonding a semiconductor device on a die pad electrode portion of a lead frame, solder material containing lead (for example, (Sn—Pb)-based solder material containing Pb of 85% or more by mass) has been used, but use of Pb-free solder material has been required even in the die-bonding solder material.
Here, in a case of solder material containing Pb of 85% or more by mass, they often have a solidus temperature of 260 degrees C. or more, which is a relatively high temperature, so that it has been conceivable that such a high temperature has exerted a bad influence upon the circuit element such as the semiconductor device. This is because a heating temperature to be used in a reflow furnace in this case is the solidus temperature (260 degrees C.) or more so that soldering is performed under a condition such that cracks occur in the portion bonded by the solder material or the die pad electrode portion or exfoliation occurs in an interface between the lead frame and a mold.
From these points of view, as the die-bonding solder material to be used for bonding the circuit element on the lead frame, studies by which Pb-free solder material having low melting temperature can be used have been carried out.
As the lead-free solder material having a lower solidus temperature than that of the solder material containing lead, (Sn—Ag)-based solder material, (Sn—Cu)-based solder material, (Sn—Sb)-based solder material and the like have been known. Among them, as the solder material having a high melting point and a higher solidus temperature than the heating temperature used in the reflow furnace, (Sn—Sb)-based solder material having high melting point has been known (see Patent Document 1).
In the (Sn—Sb)-based solder material having the high melting point, which is disclosed in Patent Document 1, its composition ratio is devised to prevent any voids or the like from occurring in a bonded portion by the solder material having the high melting point, which has been used at a period of die bonding time, even at a heating temperature when mounting a surface-mount component (IC package) on a printed circuit board.